1. Technical Field of the Invention
The present invention relates generally to bi-directional valves for high pressure fluid flow and, more particularly, to a bi-directional shut-off trim for a valve which possesses the functional attributes of a pilot operated trim and a balanced trim through the integration of a spring loaded check valve into a pilot trim. In forward flow isolation, the bi-directional shut-off trim of the present invention acts as a normal pilot operated trim. In reverse flow, the check valve of the shut-off trim opens to balance the pressure on either side of the plug thereof.
2. Description of the Related Art
There is known in the prior art valve constructions which are adapted to provide pressure balance on opposite sides of a main valve assembly during both opening and closing movements of the main valve assembly with fluid flow in either direction through the valve. One such exemplary prior art bi-directional balanced valve is disclosed in U.S. Pat. No. 3,888,280 entitled BI-DIRECTIONAL PRESSURE BALANCED VALVE issued Jun. 10, 1975.
However, currently known valve constructions or designs providing a bi-directional pressure balanced function are often subject to early failure and malfunctioning when used under severe service conditions, e.g., under high temperature and high pressure operating conditions. More particularly, the failure or malfunctioning of currently known valve designs is often attributable to the rapid erosion of deterioration of their sealing areas, as well as other critical valve components. In this regard, the available seal materials usable in conjunction with currently known bi-directional pressure balanced valve designs are often not adequate for providing required shut-off characteristics, and further frequently make the valve susceptible to early failure when the such seal materials are subjected or exposed to the intended operational environment of the valve.
The present invention is intended to represent an improvement to existing bi-directional pressure balanced valve designs by providing a valve shut-off trim which combines a pilot operated trim and a balanced trim through the addition of a spring loaded check valve within the pilot trim. As indicated above, in forward flow isolation, the shut-off trim of the present invention acts as a normal pilot operated trim, while in reverse flow, the check valve thereof opens to balance the pressure on either side of the plug of the trim. Thus, the addition of the spring loaded check valve in the shut-off trim of the present invention causes the pilot operated trim to act as a balanced plug in the reverse flow direction. These, as well as other features and advantages of the present invention, will be described in more detail below.